1. Field of the Invention
The invention relates to an actuator capable of minutely moving a movable body with respect to a fixed body by electrowetting.
2. Description of Related Art
Electrowetting is known as a phenomenon in which, when potential difference is applied between an electrode covered by an insulating layer and a liquid droplet resting on a surface of the insulating layer, a wetting angle (i.e., a contact angle) of the liquid droplet with respect to the surface of the insulating layer is changed due to changes in interfacial tension between the liquid droplet and the surface of the insulating layer. If electrowetting is applied to various drive devices, the drive devices drive with less electric power as compared with known devices employing electric motors or piezoelectric actuators. Further, the drive device employing electrowetting is smaller than such known devices.
For example, as described in Japanese Laid-open Patent Publication No. 2005-185090, electrowetting is applied to a device driven when a focus of a camera lens is adjusted. The device includes a first structure body and a second structure body disposed opposite to the first structure body to move toward or away from the first structure body and such that a liquid droplet disposed between the first and second structure bodies contacts the first and second structure bodies.
The first structure body includes a first electrode, an insulating layer formed on a surface of the first electrode, and a first liquid repellent layer covering the insulating layer on its surface opposite to the second structure body. The second structure body includes a second electrode and a second liquid repellent layer surrounding the second electrode on its surface opposite to the first structure body. The liquid droplet contacts the second liquid repellent layer and the second electrode at all times. When a voltage is placed between the first electrode and the second electrode with which the liquid droplet is in contact, a contact angle of the liquid with respect to the surface of the first liquid repellent layer which the liquid droplet contacts is changed by electrowetting. Thus, a height of the liquid droplet between the first and second structure bodies is reduced, so that a distance between the first and second structure bodies is decreased. In this manner, the first structure body moves toward the second structure body.